The present invention relates to an apparatus for controlling a switch connecting a power supply to a load. More particularly, the apparatus controls the switch based on the output voltage levels of the power supply.
Referring to FIG. 1, there is shown a schematic diagram of a prior art. The prior art connects the coil 3 of a solenoid switch 2 directly to the power line. Due to the characteristics of the electromagnet in the solenoid switch 2, the solenoid switch 2 would be engaged when the output voltage of the power supply 1 has reached 65-75% of the rating value. The solenoid switch 2 is in a holding state after being engaged. In the holding state, the silicon steel magnetic cores come in contact with each other such that the gap therebetween is reduced and whereby the magnetic reluctance thereof is decreased. Therefore, the solenoid switch 2 would be disengaged only when the output voltage of the power supply 1 has dropped below 35-40% of the rating value.
Since the solenoid switch would be engaged when the output voltage of the power supply has reached 65-75% of the rating value, the power received by the load at this instant is thus 25-35% lower than its rating value. This low power may drive the load in an inadequate manner and somehow cause certain adverse effects to the load.
Moreover, in some cases, the voltage input to the load may become overhigh to the load. Should this happens, the solenoid switch should be disengaged to cut off the power. Unfortunately, the prior art is not capable of doing so. Therefore, under such a condition, the load would run a risk of being damaged by the overhigh voltage.